Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: David Cooper on 08/08/2014 20:25:18
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I heard a case long ago about a person who was struck by lighting and had a burn right down his front, but with a two inch gap in it where the current had run through the metal strip in a banknote. This led me to wonder if having a small amount of wiring in clothes would save lives. There may be a danger that it would make you more likely to be struck, but that's probably a marginal difference, and if you are struck it would stop the current running through your heart, which is the main killer.
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Do you saw Dr Megavolt performances?
He has cloth made of metal wires around all his body.
(https://c1.staticflickr.com/1/93/235564499_2084af8aab.jpg)
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I saw people wearing clothing like that on a TV science program where they were working on live power cables up a pylon. The question is though, would something less substantial (like a few thin wires) do the job to a reasonable degree? The metal strip in the bank note makes me think it might, but it wouldn't be a good idea to do the experiment if it doesn't work well enough to offset any increased risk in being struck.
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Isn't it because he was wearing a Faraday cage.
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The suit in the picture is indeed a faraday cage, but it's usually said that a car is a faraday cage too and is safe in a thunderstorm, despite the big gaps in it where the windows are. Maybe a car isn't 100% safe, but it must be close to that. If you can create a path of low resistance past you and down to the ground, the lightning should take it instead of going through you. If the lightning comes to you from one side and you have a wire at the other side, it may go through you to reach the wire, but if you have a wire on the side the lightning strike comes from as well, most of all of the current is more likely to go down that instead. I was imagining four wires so that all sides are covered. You could still have a path burned through your head but keeping it away from your heart would provide the biggest gain, while wires down the outside edges of trousers could prevent damage lower down, ideally having a bit of wire almost trailing on the ground to avoid a hole being burned through your foot. I think all of that would work, but no one's produced clothing of this kind for ordinary people, so maybe there's a problem with the idea which has led to it being ruled out.
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It may not be an idea that people are comfortable with. The wires could break and stab the skin. Do the benefits outweigh the drawbacks.
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The metal strip in a banknote is less substantial than the wires in earphones, and people are happy to wear those. I was picturing a few wires of that kind built into clothing, and particularly outdoor gear intended for use in rain where the wires wouldn't be noticed. They wouldn't need to be greatly robust as a few breaks would make no practical difference to their effectivenes, but if they're in any clothes that go through a washing machine, they'd need to be encased in something that will protect them and also protect other fibres from them. I'd have thought the size of the golf market would drive the development of such clothing, but it doesn't appear to have happened yet.
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From commercial point of view, quantity of people hit by lightning per year is very small, to make market for lightning-safe clothing.
Unfortunately, yet another time evil money wins battle with life...
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At the Museum of Science in Boston there is a Van de Graaff generator which generates a few million volts for their lighting exhibit. A man stands inside a cage which is like a bird cage with wire strips rather than encased entirely of sheet metal and he's protected. See
http://www.mos.org/live-presentations/lightning
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Assuming the clothing is designed for one-time use ("replace after being struck by lightning"), you could make the wires quite thin. [After all, seatbelts carry warnings that they should be replaced after each accident...]
A metal strip in a banknote would turn into plasma when hit with any reasonable lightning bolt. The plasma has very low impedance, and it only has to survive a few tens of microseconds to carry the bulk of the current. In future, metallic carbon nanotubes could act as a flexible conductive path that turns into a plasma (once the price of carbon nanotubes comes down significantly!)
The alternative of having a multiple-use suit which could survive multiple lightning strikes would call for a copper braid, perhaps 1 inch (2-3cm) wide and 1/4 inch (5mm) thick, running from the top of your head and down both legs. The price of carbon nanotubes is expected to come down, but the price of copper will only rise.
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I heard a case long ago about a person who was struck by lighting and had a burn right down his front, but with a two inch gap in it where the current had run through the metal strip in a banknote. This led me to wonder if having a small amount of wiring in clothes would save lives. There may be a danger that it would make you more likely to be struck, but that's probably a marginal difference, and if you are struck it would stop the current running through your heart, which is the main killer.
My question is what kind of safety that you're looking for? Are you looking for safety where you get no burn at all? Burn but no danger of death etc?
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I seems the idea was popular in France a while ago.
http://tpefoudre-wimshurst.pagesperso-orange.fr/Lhomme_et_la_foudre_a_travers_le_temps.html
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If it's raining and the person who is being struck by lightning is soaked, the current tends to flow across the skin rather than going inside the body, so they tend to survive and get lightning-pattern burns all across their skin. The metal wire idea would probably do the same, but without the burns, and without the need to be soaked. I was listening to a BBC World Service program the other night in which a man described what happened to him when he was struck by lightning, and in his case it did a lot of lasting internal damage which is still making his life hard; damage which may have been avoidable.
The odds of being struck are clearly very low, but not so low that you can feel happy about being caught in a thunderstorm. Crouching on the ground for an hour in the pouring rain would generally be lethal where I live if you're wearing the wrong gear, so it isn't always a realistic option, but I've long wondered if it would be practical to put wiring into many kinds of clothing, hidden within seams. It wouldn't need to survive beyond a single lightning strike as people are usually only hit once per storm. There's no need to try to prevent surface burns either: it's just the internal damage that needs to be avoided, and the nasty exit wounds too where it can burn a hole through both your thick rubber boot and your foot.
The main concern I have with the idea though is whether it would make you more likely to be struck. Golfers tend to get hit when they raise a golf club up, the rounded metal head providing a perfect object for the strike to land on. Lightning conductors on buildings are sharp so that they repel lightning rather than attracting it, so if the wires in clothing meet at the top in curved loops, that might attract a strike to you, but if the different wires don't meet up, they might act as spikes and make you less likely to be hit. I'm just guessing on that point though - I'd love to get access to Dr Megavolt's apparatus to try things out (though on a mannequin, obviously) and see what actually happens. Serious rain gear should maybe have a long extendible sharp-pointed aerial built into it which can be extended in a thunderstorm, thereby repelling lightning, or at least making it strike far enough away from your ears to prevent the worst hearing damage.
Anyway, I'm sure something could be designed that would make a significant difference, and it could be built into outer garments and sports clothing as standard without astronomical cost. I'd certainly buy it if it was available and if it could be shown to offer significant protection. In the meantime though, I'd like to experiment with wires, but I don't want to get things wrong and end up making it more dangerous instead of safer.
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wires in clothes which direct the plasma into the ground (around you) "might" protect you from electrocution but the wires would most likely fry upon impact which would burn you (to death) and fling fast moving high amp sparks into your flesh like tiny fragments of a grenade.
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keeping it away from your heart would provide the biggest gain
I agree that this is important for avoiding immediate death, but I have heard that people have suffered considerable neurological problems for many years afterwards.
The "skin effect (http://en.wikipedia.org/wiki/Skin_effect)" means that rapidly changing (high frequency) currents create magnetic fields which tends to concentrate the current on the outside of a wire. I assume that the same would apply to human bodies too, tending to concentrate the current in the skin, rather than the heart.
golf club ... the rounded metal head providing a perfect object for the strike to land on. Lightning conductors on buildings are sharp so that they repel lightning
Apparently, there is considerable debate (http://en.wikipedia.org/wiki/Lightning_rod#Should_a_lightning_rod_have_a_point.3F) about whether rounded or sharp is a better shape to attract lighting.
To my simple way of thinking, a sharp point has a small radius of curvature and a greater electric field gradient. This gradient would tend to ionise the air via corona discharge, creating a larger conductive sphere around the point.
I guess the question is whether the ionised conductive sphere is an easier lightning target than a metal conductive sphere...
In planning lightning protection, a "rolling sphere (http://en.wikipedia.org/wiki/Lightning_rod#Lightning_protection_system_design)" of 46 meters radius is often used. So perhaps it doesn't matter whether it is a point or a rounded rod, provided the rolling sphere considers it the most exposed point?
I expect that advertising "Lightning resistant clothing" would create a significant legal minefield.
- Even if it reduced injury & mortality by 90%, you would still "lose your shirt" to the other 10%.
- Wearing lightning resistant clothes is likely to produce risky behaviours which may increase the chance of being struck by an order of magnitude - enough to offset any protection provided.
There are also many many paths by which you could be struck:
- We tend to think of getting hit on the head, with exit through the feet.
- But people have also been sheltering beside a treetrunk, and lightning finds a human a lower impedance than a treetrunk - and so they get struck on their back
- There is the umbrella/golf-club scenario where the bolt enters via the hand
- There is earth potential rise (https://www.youtube.com/watch?v=u_6b6Bk6bM8), where a nearby lightning strike causes a very high voltage between your feet, so the current flows in one foot, and out the other.
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keeping it away from your heart would provide the biggest gain
I agree that this is important for avoiding immediate death, but I have heard that people have suffered considerable neurological problems for many years afterwards.
Ideally you don't want it to pass through any part of you at all, but if you're wearing shorts you're not going to want wires connecting them to your socks, so you just have to accept that it'll burn through one or both of your legs for a stretch. The head's also awkward - it could be protected by a wire sticking up, but no one would want it there unless they're already in a thunderstorm. If it's raining though and wires are built into hoods, it would make the wearer safer without having to think about taking action.
The "skin effect (http://en.wikipedia.org/wiki/Skin_effect)" means that rapidly changing (high frequency) currents create magnetic fields which tends to concentrate the current on the outside of a wire. I assume that the same would apply to human bodies too, tending to concentrate the current in the skin, rather than the heart.
That doubtless helps to a degree, but there's a substantial difference in the death rate between soaked and dry people being struck by lightning, according to documentaries on the subject, at least (though maybe I shouldn't be trusting them).
golf club ... the rounded metal head providing a perfect object for the strike to land on. Lightning conductors on buildings are sharp so that they repel lightning
Apparently, there is considerable debate (http://en.wikipedia.org/wiki/Lightning_rod#Should_a_lightning_rod_have_a_point.3F) about whether rounded or sharp is a better shape to attract lighting.
A few experiments with Dr Megavolt's apparatus ought to be able to provide practical answers. If the lightning's going to hit you anyway, it would be best to attract it to the safest place rather than repelling it from the aerial over your head such that it hits your head instead.
I expect that advertising "Lightning resistant clothing" would create a significant legal minefield.
Cycle helmets cause more accidents and it appears to cancel out the advantage of wearing them, but people don't sue the manufacturers for the extra accidents they have. They simply accept that a helmet may save their life in one accident and cost it in another - it is for them to judge for themselves whether they are likely to be better off wearing it and they play the odds as best as they can calculate them, taking into account the kind of cycling they do and the dangers they generally encounter.
Even if it reduced injury & mortality by 90%, you would still "lose your shirt" to the other 10%.
That doesn't happen with other safety gear, even when the benefits aren't substantial. In the case of this lightning-diverting clothing, so long as it doesn't attract more hits, the advantage of wearing it should be considerable, and it may be better to have a 1% greater risk of being struck if the risk of death from being struck is reduced by >99%.
Wearing lightning resistant clothes is likely to produce risky behaviours which may increase the chance of being struck by an order of magnitude - enough to offset any protection provided.
It could do, as happens with cycle helmets, but there are cases like cycle racing where helmets do not make cyclists take substantially greater risks because they'd typically be going flat out regardless. Golfers do not stay out in lightning, but this kind of clothing could change that for foolish ones and put more commercial pressure on professionals to keep playing in dangerous conditions, but the damage to hearing caused by being struck by lightning is good enough reason in itself not to play games with thunderstorms. What I don't like is getting caught in one by surprise while on a long cycle run, while hillwalking or when sailing. These things happen, and it would be good to be armed against the risk of unnecessary death.
There are also many many paths by which you could be struck... We tend to think of getting hit on the head, with exit through the feet... But people have also been sheltering beside a treetrunk, and lightning finds a human a lower impedance than a treetrunk - and so they get struck on their back
Wherever it comes from, the path of least resistance should soon lead it onto a wire. If you made clothing out of conductive fibres, you'd then have all-round protection without the gaps, so that could be even safer, though again you don't want to attract lightning, so that needs to be experimented with to see if it does and if it wipes out the gains. It is unlikely that it does significantly increase the risk of being struck.
There is the umbrella/golf-club scenario where the bolt enters via the hand
You could lose the use of an arm if that isn't wired too, but it would follow the wires beyond that, and it's better to lose an arm and a leg than to be killed.
There is earth potential rise (https://www.youtube.com/watch?v=u_6b6Bk6bM8), where a nearby lightning strike causes a very high voltage between your feet, so the current flows in one foot, and out the other.
That could do a fair bit of damage, but it's more dangerous to four-legged animals as it puts their heart on the path, and the further apart the legs (front to back) the higher the voltages that cross it. Having wires up and down your trousers could cause damage to you that you wouldn't have suffered otherwise, but in a thunderstorm you can reduce the danger from this by taking short steps or by making sure only one foot is in contact with the ground at a time.
Ultimately it all comes down to statistical advantage and whether its saver to have something or safer without it. It's the same with computer-driven cars where they will reduce the death rate enormously, but the odd one might go wrong and mow someone down. That will happen at some point and there will immediately be an outcry against them, but human drivers frequently malfunction and mow people down without those same people calling for all human drivers to be banned. Their reaction is irrational (they're already complaining before it's even happened, so these people do exist), but the statistics will not back them up. Is it safer on average? Yes, then do it / no, then don't do it.
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I seems the idea was popular in France a while ago.
http://tpefoudre-wimshurst.pagesperso-orange.fr/Lhomme_et_la_foudre_a_travers_le_temps.html
Some good pictures there, including the fulgurite half way down. You can see why the wires dangling from umbrellas went out of vogue though; they'd always be getting in the way and the odds against being struck while using one are too low for people to keep putting up with them. You want something that you can forget is there. (Thanks for the French reading practice too - learned a few new words from that.)
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If you can create a path of low resistance past you and down to the ground, the lightning should take it instead of going through you.